Optical compensation film, viewing angle compensation integral type polarizing plate and liquid crystal display apparatus

ABSTRACT

An optical compensation film comprising a cellulose ester film is disclosed. In the film, (a) each of photoelastic coefficient C(md) in a mechanical direction and photoelastic coefficient C(td) in the transverse direction of the cellulose ester film is 1×10 −9  to 1×10 −13  Pa −1  and C(md)&lt;C(td), (b) retardation R 0  within the plane of the cellulose film defined by Formula (I) is 20 to 70 nm, (c) retardation R t  of the cellulose ester film in a thickness direction, defined by Formula (II) is 70 to 400 nm, and (d) both of a dimensional variation ratio S(md) in the mechanical direction and a dimensional variation ratio S(td) in the transverse direction of the cellulose ester film prior to and after being allowed to stand at ambient conditions of 80° C. and 90 percent relative humidity for 50 hours are − 1  to  1  percent, and |S(md)|&gt;|S(td)|.

BACKGROUND OF THE-INVENTION

[0001] The present invention relates to an optical compensation film, anoptical compensation film support, a viewing angle compensation integraltype polarizing plate, and a liquid crystal display apparatus.

[0002] Currently, cellulose acetate film (represented by cellulosetriacetate film) is widely employed to prepare silver halidelight-sensitive photographic materials as well as optical films due toits desirable characteristics such as high transparency as well asminimal optical drawbacks. Particularly, cellulose acetate film ispreferably employed as a polarizing plate protective film for liquidcrystal display apparatuses.

[0003] Incidentally, when images on a crystal liquid display apparatusare viewed from an oblique direction, image quality is degraded comparedto that when viewed directly from the front. The resulting imagedegradation is due to viewing angle characteristics inherent in liquidcrystal display apparatuses. In order overcome this drawback, aneffective method is known in which viewing angle compensation film isarranged between the liquid crystal cell and the polarizer (refer, forexample, to Japanese Patent Publication Open to Public Inspection Nos.2000-154201 and 2002-156527).

[0004] However, it has been found that problems are not completelysolved employing the aforesaid method.

[0005] (Patent Document 1)

[0006] Japanese Patent Publication Open to Public Inspection No.2000-154201

[0007] (Patent Document 2)

[0008] Japanese Patent Publication Open to Public Inspection No.2002-156527

[0009] The inventors of the present invention conducted investigationsin an attempt to solve the aforesaid problems. As a result, JapanesePatent Application No. 2002-322923 was submitted. The patent applicationdiscloses markedly effective techniques described below. In the viewingangle compensation integral type polarizing plate, stated in thespecification of the aforesaid patent, an appropriate phase differencecompensation function is given to a polarizing plate protective film.Consequently, the production process is abbreviated to allow the viewingangle compensation film to adhere to the polarizing plate. As a result,it is possible to simplify the production process and to decrease thethickness of liquid crystal display apparatuses. However, in theaforesaid invention, since film is oriented in the transverse (td)direction (or lateral direction), residual strain remains. The aforesaidresidual strain results in dimensional variation during storage. As aresult, in practice, critical problems have occurred in which thepolarizing plate, adhered onto the liquid crystal cell, peels off.

[0010] In order to overcome the aforesaid problems, a method isconsidered in which physical dimensional variation is minimized, forexample, by increasing the adhesion force of an adhesive which adheres aliquid crystal cell to a polarizing plate. This technique minimizesphysical dimensional variation, but the film is apparently in a state oforientation or contraction, resulting in a state in which stress isapplied to the film. The resulting stress varies the retardation of thefilm and markedly affects viewing angle compensation characteristicsduring storage. As a result, in view of durability of the viewing anglecharacteristics, critical problems have practically occurred.

SUMMARY OF THE INVENTION

[0011] An objective of the present invention is to provide an opticalcompensation film which exhibits excellent viewing angle compensationfunction and also to provide an optical compensation film supportcapable of enhancing durability of the viewing angle compensationfunction during storage, an optical compensation film, a viewing anglecompensation integral type polarizing plate, and a liquid crystaldisplay apparatus.

[0012] The objective of the present invention was achieved as describedbelow.

[0013] (1) An optical compensation film comprising a cellulose esterfilm comprising cellulose ester wherein

[0014] (a) each of photoelastic coefficient C(md) in a mechanicaldirection and photoelastic coefficient C(td) in a transverse directionof the cellulose ester film is 1×10⁻⁹ to 1×10⁻¹³ Pa⁻¹, and C(md)<C(td),

[0015] (b) retardation R₀ within a plane of the cellulose film definedby Formula (I) is 20 to 70 nm,

[0016] (c) retardation R_(t) of the cellulose ester film in a thicknessdirection defined by Formula (II) is 70 to 400 nm, and

[0017] (d) each of a dimensional variation ratio S(md) in the mechanicaldirection and a dimensional variation ratio S(td) in the transversedirection of the cellulose ester film prior to and after being allowedto stand at ambient conditions of 80° C. and 90 percent relativehumidity for 50 hours are −1 to 1 percent, and |S(md)|>|S(td)|.

R ₀=(nx−ny)×d  (I)

R_(t)={(nx+ny)/2−nz}×d  (II)

[0018] wherein nx is a refractive index in a transverse direction withina film plane, ny is a refractive index in a mechanical direction, nz isa refractive index in a thickness direction of the film, and d is athickness of the film in nm.

[0019] (2) The optical compensation film, described in (1), whichcomprises at least one optically anisotropic layer.

[0020] (3) The optical compensation film, described in (1) or (2),wherein cellulose ester of the cellulose ester film simultaneouslysatisfies Formulas (IV) and (V) given below.

2.55≦X+Y≦2.85  (IV)

1.4≦X≦2.85  (V)

[0021] wherein X is the degree of substitution of an acetyl group and Yis a degree of substitution of a propionyl group and/or a butyryl group.

[0022] (4) The optical compensation film, described in any one of (1) to(3), wherein the cellulose ester of the cellulose ester film has adegree of acetylation of 59.0-61.5 percent, and comprises a compoundhaving at least two aromatic rings in an amount of 0.1 to 20 parts byweight with respect to 100 parts by weight of cellulose ester.

[0023] (5) The optical compensation film, described in any one of (2) to(4), wherein the optically anisotropic layer has a fixed nematic hybridorientation structure.

[0024] (6) The optical compensation film, described in any one of (2) to(5), wherein the optically anisotropic layer contains a liquid crystalcompound.

[0025] (7) In a viewing angle compensation integral type polarizingplate comprised of two protective films and a polarizer, a viewing anglecompensation integral type polarizing plate wherein at least one of saidprotective films is an optical compensation film, described in any oneof (1) to (6), and the delayed phase axis of the ester film in saidoptical compensation film and the transparent axis of said polarizer aresubstantially parallel.

[0026] (8) A liquid crystal display apparatus employing the viewingangle compensation integral type polarizing plate described in (7).

[0027] (9) A support for an optical compensation film wherein

[0028] (a) each of photoelastic coefficient C(md) of a cellulose esterfilm in the mechanical direction and photoelastic coefficient C(td) ofthe same in the transverse direction is 1×10⁻⁹ to 1×10⁻¹³ Pa⁻¹ andC(md)<C(td),

[0029] (b) retardation R₀ within the plane of said cellulose filmdefined by Formula (I) is 20 to 70 nm,

[0030] (c) retardation R_(t) of said cellulose film in the thicknessdirection, defined by Formula (II) is 70 to 400 nm, and

[0031] (d) dimensional variation ratio S(md) of film in the mechanicaldirection and dimensional variation ratio S(td) of film in thetransverse direction prior to and after being allowed to stand atambient conditions of 80° C. and 90 percent relative humidity for 50hours are −1 to 1 percent, and |S(md)|>|S(td)|.

R ₀=(nx−ny)×d  (I)

R _(t)={(nx+ny)/2−nz}×d  (II)

[0032] wherein nx is the refractive index in the delayed phase axisdirection (the transverse direction) within the film plane, ny is therefractive index in advanced phase axis direction, (mechanicaldirection), nz is the refractive index in the thickness direction offilm, and d is a thickness of film.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0033] Generally, liquid crystal display apparatuses exhibit viewingangle characteristics. When viewed from an angle with respect to thenormal to the liquid crystal cell, a problem has occurred in which imagecontrast decreases. In order to solve the aforesaid problem, it is knownthat it is effective to arrange a phase difference film (an opticalcompensation film) having suitable retardation between the liquidcrystal cell and the polarizer. Generally, it is preferable thatretardation (R₀) in the in-plane direction is 20 to 70 nm, andretardation (R_(t)) in the depth direction is 70 to 400 nm.

[0034] When the retardation of cellulose ester film is controlled, thedegree of substitution of employed cellulose ester and the type ofsubstituents are critical. In the present invention, suitableretardation is possible for the optical compensation polarizing plate(the viewing angle compensation integral type polarizing plate) byemploying cellulose ester which satisfies 2.55≦X+Y≦2.85 and 1.4≦X≦2.85,wherein X represents the degree of acetyl substitution and Y is thedegree of substitution of a propionyl group and/or a butyryl group andby orienting the resulting film.

[0035] Further, in the present invention, it is possible to result insuitable retardation as the viewing angle compensation cellulose esterfilm by orienting cellulose ester film which comprises compoundsexhibiting the degree of acetylation of cellulose ester of 59.0 to 61.5percent and have at least two aromatic rings in an amount of 0.1 to 20parts by weight with respect to 100 parts by weight of cellulose esterfilm.

[0036] Still further, in order to improve viewing angle characteristicsof a liquid crystal display panel, known to be effective is to arrange alayer comprising rod-shaped or disc-shaped liquid crystal compounds inan optical compensation cellulose ester film having suitable phasedifference. Namely, it is possible to further improve the viewing anglecharacteristics by employing an optically anisotropic layer in which anematic hybrid structure is formed by orienting rod-shaped liquidcrystal molecules or by arranging a disc-shaped liquid crystal moleculelayer.

[0037] In order to improve the viewing angle characteristics of liquidcrystal display apparatuses, from the viewpoint of minimizing lightleakage, when black is displayed, it is critical that the delayed phaseaxis of the optical compensation cellulose ester film and thetransmission axis of the polarizer are substantially parallel or atright angles to each other. Further, as noted above, it is possible toimprove the viewing angle characteristics by applying opticallyanisotropic layer comprising liquid crystal compounds onto a celluloseester film. In such a case, it is markedly preferable that the delayedphase axis of the cellulose ester film and the delayed phase axis of theoptically anisotropic layer are at right angles to each other.

[0038] When industrial mass-production of liquid crystal displayapparatuses is considered, in order to form an optically anisotropiclayer comprising optically anisotropic compounds by coating liquidcrystal compounds and allowing those to be oriented, it is required thatthe cellulose ester film is subjected to rubbing in a rolled state.However, it is very difficult to carry out rubbing in the transversedirection, while it is much easier to carry out rubbing in themechanical direction (the direction of movement). On the other hand, inorder that this and the delayed phase of the cellulose ester film are atright angles to each other, it is preferable that orientation is carriedout in the transverse direction. When polarizers are prepared employingorientation, orientation at mechanical direction is preferred. As aresult, the absorption axis of the polarizer is in the mechanicaldirection while the transmission axis is in the transverse direction. Asa result, it is preferable that the delayed phase axis of the viewingangle compensation cellulose ester film and the transmission axis of thepolarizer are substantially parallel.

[0039] Further, in order to improve the viewing angle, it is preferablethat nematic type polymer liquid crystal compounds are incorporated intothe optically anisotropic layer so that a structure is formed in whichhybrid orientation is achieved in which the pre-tilt angle of the liquidcrystal molecules varies in the depth direction.

[0040] The variation of viewing angle characteristics over time storageis due to the variation of retardation over time. Based on investigationresults obtained by the inventors of the present invention, specialattention was paid to anisotropy of the photoelastic coefficient anddimensional variation, whereby the present invention was achieved. It isconsidered that the photoelastic coefficient responds to the retardationvariation for stress, and the dimensional variation is the valuerelating to the magnitude of stress applied to film over time. Forexample, when a cellulose ester film is oriented in the transverse (td)direction, the absolute value of dimensional variation in the transversedirection over time is greater than that in the mechanical (md)direction, and the photoelastic coefficient in the transverse directionfurther increases. It is considered that the greater the photoelasticefficient and the absolute value of the dimensional variation, thegreater the variation of retardation becomes. The td direction issubjected to greater variation due to synergistic effects of these two,compared to the md direction. As a result, the variation of viewingangle over time increases, resulting in a film with insufficientdurability. In the present invention, durability of viewing anglecompensation function was improved by decreasing the absolute value ofdimensional variation in the direction of greater photoelasticcoefficient in such a manner that strain remaining in the orientationdirection was relaxed, for example, by appropriately applying heat afterorientation.

[0041] Further, substantially parallel, as described in the presentinvention, means that deviation from the parallel is allowed in therange which results in no problems, and the angle of the axis of asubject is within approximately ±10 degrees, is preferably within ±3degrees, and is more preferably ±1 degree. On the other hand, at rightangles to each other means that a range near 90 degrees is allowed, andthat range is preferably about 80 to about 100 degrees, is morepreferably 85 to 95 degrees, and is most preferably 90 degrees.

[0042] The present invention will now be detailed.

[0043] (Casting of Cellulose Ester Film)

[0044] A casting method of the cellulose ester film according to thepresent invention will be described (as a representative example, usinga solution extrusion casting method).

[0045] (1) Dissolving Process:

[0046] In a dissolving tank, a dope is prepared by dissolving, whilestirring, cellulose ester in organic solvents comprised of good solventsfor cellulose ester as a main component. Dissolution is carried outemploying various dissolving methods in which dissolution is carried outat a temperature lower than the boiling point of the main solvent undernormal pressure, dissolution is carried out at a temperature higher thanthe boiling point of the main solvent under a pressurized state,dissolution is carried out while chilled at 0° C. or lower, ordissolution is carried out under high pressure. In the presentinvention, any of these methods may be preferably employed. However, thehigh temperature dissolving method is more preferably employed in whichdissolution is carried out at a temperature higher than the main solventunder a pressurized state. After dissolution, the resulting dope isfiltered employing a filter, defoamed and conveyed to the subsequentprocess employing a pump.

[0047] Into a dope, it is possible to incorporate additives such asplasticizers, antioxidants, UV absorbers, matting agents, or retardationincreasing agents which exhibit various desirable functions. Theseadditives may be added together with cellulose ester and solvents whenthe dope is prepared, or may be added during or after preparation of thedope. Further, added may be thermal stabilizers such as salts ofalkaline earth metals, antistatic agents, fire retardants, slippingagents, and lubricants.

[0048] (2) Extrusion Process: The dope is conveyed to a pressure diethrough a pressure type quantitative gear pump, and is extruded at theextrusion position onto a specular surface metal endless belt whichconveys the extrusion or a revolving metal drum (hereinafter referredsimply to as a metal support) from the pressure die. In an extrusionapparatus employing a die, a pressure die is preferred in which the slitshape of a mouth ring portion can be controlled and which is capable ofeasily making the web thickness uniform. Pressure dies include a coathanger type and a T die, which are preferably employed. In order toincrease the casting rate, two pressure dies may be arranged above themetal support and multilayer coating may be carried out while dividingthe dope into several portions.

[0049] (3) Solvent Evaporation Process: The web on the metal support isheated so that organic solvents are evaporated. Methods to evaporateorganic solvents include a method in which air is blown from the webside and/or heat is transmitted from the back surface of the metalsupport employing a liquid, and a method in which heat is transmittedfrom the front and back surfaces employing radiated heat. Any of thesemethods may preferably be employed.

[0050] (4) Peeling Process: A web which has been subjected tovaporization of organic solvents on the metal support is peeled from themetal support. The peeled web is conveyed to the following dryingprocess. At the time of peeling, when the residual solvent amount(described below) of the web is excessive, peeling becomes difficult. Onthe contrary, when the web is peeled after being sufficiently dried onthe metal support, a part of the web occasionally separates duringpeeling.

[0051] Methods to increase the casting rate include gel casting whichmakes it possible to peel in the presence of a large amount of residualsolvents, a method in which poor solvents for cellulose ester are addedto a dope and after extrusion of the dope, the resulting web is gelled,and a method in which the temperature of the metal support is lowered toresult in gelling. When gelling is carried out on the metal support, theresulting layer strength increases. As a result, it is possible to carryout peeling even though solvents remain in relatively large amounts.Consequently, it is possible to carry out peeling earlier to enable anincrease in a casting rate. In the case in which peeling is carried outwith an excessive amount of solvents, when the web is excessively soft,flatness is degraded during peeling, and wrinkling and longitudinalstreaking tend to form due to peeling tension. As a result, the residualsolvent amount at peeling is determined while taking into account theeconomic rate and the resulting quality. In the present invention, it ispreferable that peeling is carried out at a residual solvent amount of10 to 120 percent by weight.

[0052] (5) Drying Process:

[0053] A web is dried employing a drying apparatus in which the web isconveyed while alternatively passed through guide rollers arranged inzigzag and/or a tenter drying apparatus in which the web is conveyedwhile both edges of the web are gripped by clips. A drying means isgenerally such that hot air is blown onto both sides of the web, but ameans is possible in which instead of blown air, heating is carried outby exposure to microwaves. Excessively rapid drying tends to degradeflatness of the finished film. Over the entire drying process, dryingtemperature is preferably 40 to 250° C., and is more preferably 70 to180° C. Drying temperature, drying air amount, and drying time varydepending on solvents employed. Drying conditions may be appropriatelychosen corresponding to types and combinations of the employed solvents.

[0054] After peeling from the metal support surface, in the dryingprocess, the web tends to be subjected to contraction in both directionsdue to evaporation of solvents. When drying is carried out more rapidlyat higher temperature, the resulting contraction increases. It ispreferable to carry out drying while minimizing the contraction as toresult in the desired flatness of the finished film. From thisviewpoint, a method (a tenter system) is preferred in which in theentire drying process or one part of the drying process, drying iscarried out while holding both edges of the web clipped in thetransverse direction, as shown, for example in Japanese PatentPublication Open to Public Inspection No. 62-46625. In such a case, itis possible to control retardation by controlling the orientation factorof the web, the residual solvent amount, and the temperature.

[0055] In the present invention, it was possible to provide suitableretardation for viewing angle compensation by setting, for example, theresidual solvent amount of film at 5 to 30 percent by weight, thetemperature during film orientation at 60 to 140° C., and theorientation factor at 1.0 to 2.0, while orienting in the transversedirection employing a tenter. Further, at that time, the transversedirection (the td direction) of the film was the nx direction, themechanical direction was the ny direction, and the thickness directionwas the nz direction. Further, at the same time, anisotropy was given tothe photoelastic coefficient and it was possible to control thecharacteristics to satisfy the formula of C(md)<C(td).

[0056] At the time, the film is in such a state that residual strain inthe td direction is greater than that in the md direction and exhibitsthe characteristic of |S(md) |<|S(td)|. Accordingly, after transverseorientation employing tenters, in order to relax the residual strain inthe td direction, the film was dried at 40 to 120° C. while conveyedemploying rollers under a tension of 50-200 N. As a result, it waspossible to prepare an optical compensation film exhibiting |S (md) |S(td)|. At that time, a critical condition is to enable relaxation in thetd direction. For example, by repeated conveyance employing at least 400rollers under the aforesaid tension at the aforesaid temperature, it waspossible to achieve characteristic conditions at the aforesaiddimensional variation ratio.

[0057] Further the optical compensation film is preferably hascharacteristics of C(td)×|S(td)|<5.0×10⁻¹⁴, and furtherC(td)×|S(td)|<C(md)×|S(md)| in view of permanence of viewing angle.

[0058] C(td) and C(md) are a photoelastic coefficient in the transversedirection and mechanical direction, respectively, in Pa⁻¹, S(td) is adimensional variation ratio in the transverse direction of the celluloseester film prior to and after being allowed to stand at ambientconditions of 80° C. and 90 percent relative humidity for 50 hours, thatis defined as (w-w₀)/w₀×100 (%), wherein w₀ is a width of the celluloseester film prior to the above processing and w is a width of thecellulose ester film after the above processing. S(md) is a dimensionalvariation ratio in the mechanical direction obtained similar to S(td).

[0059] (6) Winding Process

[0060] The dried web is wound as film. By specifying the residualsolvent amount at the completion of drying to 2 percent by weight orless and preferably 0.4 percent by weight or less, it is possible toprepare film with excellent dimensional stability. Employed as windingmethods are those which employ commonly used winders. Methods includeones such as a constant torque method, a constant tension method, ataper tension method, or an interior stress constant program tensioncontrol method, which control tension. Any of these methods may bechosen and employed.

[0061] The residual solvent amount can be expressed by the formuladescribed below.

[0062] Residual solvent amount (in percent by weight)

={(M−N)/N}×100

[0063] wherein M is the weight of a web at an arbitrary point and N isthe weight of the web having a weight of M which is dried at 110° C. forthree hours.

[0064] The thickness of a cellulose ester film varies depending on itsintended use. However, from the viewpoint of a decrease in thickness ofliquid crystal display apparatuses, the thickness of the finished filmis preferably 10 to 75 μm, is more preferably 10 to 60 μm, and is mostpreferably 10 to 40 μm. When the thickness is excessively reduced, forexample, necessary strength as a polarizing plate protective film isoccasionally not achieved. On the other hand, when the thickness isexcessively increased, the advantage of a decrease in thickness is lostcompared to the conventional cellulose ester film. It is preferable thatfilm thickness is adjusted by controlling the dope concentration, theliquid amount conveyed by the pump, the slit gap of the mouth of thedie, the extrusion pressure at the die, and the speed of a metal supportso that the desired thickness is achieved. Further, as a means toachieve uniform thickness, it is preferable to adjust the thickness insuch a manner that by employing a film thickness monitoring means,programmed feedback information is subjected to feedback to each of theaforementioned apparatuses.

[0065] Through the process from immediately after extrusion to drying inthe solution extrusion casting method, ambient air may be employed inthe drying apparatus. However, drying may also be carried out in anambience of inert gases such as nitrogen gas or carbon dioxide gas.

[0066] (Cellulose Ester Film and Its Composition)

[0067] Cellulose as a raw material of cellulose ester employed in thepresent invention is not particularly limited. Listed as raw materialsmay be cotton linter, wood pulp and kenaf. Further, cellulose esterswhich are prepared by employing these may be mixed at an optional ratioand then used.

[0068] In order to prepare film which exhibits excellent mechanicalstrength, the number average molecular weight of cellulose esteremployed in the present invention is preferably 60,000 to 300,000, andis more preferably 80,000 to 200,000.

[0069] The number average molecular weight of cellulose ester isdetermined employing high speed liquid chromatography under theconditions described below.

[0070] Solvent: acetone

[0071] Column: MPWx1 (manufactured by TOSOH Corp.)

[0072] Sample concentration: 0.2 weight/volume percent

[0073] Flow rate: 1.0 ml/minute

[0074] Sample injection volume: 300 μl

[0075] Standard sample: methyl polymethacrylate (Mw=188,200)

[0076] Temperature: 23° C.

[0077] Cellulose ester employed in the present invention is prepared byacylating cellulose raw materials. When acylating agents are acidanhydrides (such as acetic anhydride, propionic anhydride, or butyricanhydride), organic acids such as acetic acid and organic solvents suchas methylene chloride are employed and reaction is allowed to proceedemploying protonic catalysts such as sulfuric acid. When acylatingagents are acid chlorides (such as CH₃COCl, C₂H₅COCl, or C₃H₇COCl),reaction is allowed to proceed employing basic compounds such as aminesas a catalyst. Specifically, it is possible to achieve the synthesisbased on the method described in Japanese Patent Publication Open toPublic Inspection No. 10-45804.

[0078] Cellulose ester is prepared by allowing an acyl group to reactwith hydroxyl group(s) of cellulose molecules. A cellulose molecule iscomprised of the linkage of many glucose units, while the glucose unitcomprises three hydroxyl groups. The degree of substitution refers tothe number of acyl groups which are introduced into the aforesaidhydroxyl group.

[0079] Cellulose esters employed in the present invention include thosesuch as cellulose acetate propionate, cellulose acetate butyrate, orcellulose acetate propionate butyrate, in which, other than the acetylgroup, a propionyl group or a butyryl group is linked. Incidentally, thebutyryl group includes an iso-butyryl group other than an n-butyrylgroup. Cellulose acetate propionate which exhibits a greater degree ofsubstitution of the propionyl group is useful as a film for liquidcrystal display apparatuses due to its excellent water resistance.

[0080] It is possible to determine the degree of substitution of an acylgroup in accordance with ASTM-D817-96.

[0081] When the retardation as well as the photoelastic coefficient ofcellulose ester films is controlled, the degree of substitution of theemployed cellulose ester and the type of substituents become criticalfactors. In the present invention, when 2.3≦X+Y≦2.85 as well as 1.4≦X≦2.85 is satisfied, wherein X represents the degree of acetylsubstitution and Y represents the degree of substitution by a propionylgroup and/or a butyryl group, suitable retardation as a viewing anglecompensation polarizing plate (viewing angle compensation integral typepolarizing plate) tends to be obtained.

[0082] Further, in the present invention, it is possible to prepare filmexhibiting suitable retardation and photoelastic coefficient as theviewing angle compensation cellulose ester film by preparing it toexhibit a degree of acetylation of 59.0 to 61.5 percent, and to comprisecompounds having at least two aromatic rings in an amount of 0.01 to 20parts by weight with respect to 100 parts by weight of cellulose esterfilm.

[0083] (Additives of Cellulose Ester Film (Support))

[0084] In order to prepare a cellulose ester film which incorporatescompounds having at least two aromatic rings and at least two aromaticrings which exhibit a planar structure, the aforesaid compounds andcellulose ester are incorporated into a dope together with organicsolvents, and the resulting mixture is cast employing a solutionextrusion casting method.

[0085] Compounds which have at least two aromatic rings and in which atleast two aromatic rings have a planar structure may include those inwhich two aromatic rings are positioned nearly on the same plane.Namely, it is preferable that the number of π electrons is 5 to 10 whiletotaling the π electrons of two aromatic rings, aromatic heterocyclicrings, or aromatic rings including linking groups linking them.

[0086] Further, the number of aromatic rings incorporated into theaforesaid compounds is preferably 2 to 20, is more preferably 2 to 12,and still more preferably 2 to 8. The aforesaid aromatic rings includean aromatic hydrocarbon ring as well as an aromatic heterocyclic ring.The aforesaid aromatic hydrocarbon ring is most preferably a 6-memberedring (namely, a benzene ring). The aromatic heterocyclic ring isgenerally an unsaturated heterocyclic ring. The aromatic heterocyclicring is preferably a 5-membered, 6-membered, or 7-membered ring, and ismore preferably a 5-membered or 6-membered ring. The aromaticheterocyclic ring generally has the maximum number of double bonds.Hetero atoms are preferably a nitrogen atom, an oxygen atom and a sulfuratom, and of these, nitrogen atoms are particularly preferred.

[0087] Examples of aromatic heterocyclic rings include a furan ring, athiophene ring, a pyrrole ring, an oxazole ring, an iso-oxazole ring, athiazole ring, an isothiazole ring, an imidazole ring, a pyrazole ring,a furazane ring, a triazole ring, a pyran ring, a pyridine ring, apyridazine ring, a pyrimidine ring, a pyrazine ring, and a1,3,5-triazine ring. Preferably as aromatic rings are a benzene ring, afuran ring, a thiophene ring, a pyrrole ring, an oxazole ring, athiazole ring, an imidazole ring, a triazole ring, a pyridine ring, apyrimidine ring, a pyrazine ring, and a 1,3,5-triazine ring.

[0088] The bonding relationship of at least two aromatic rings may beclassified into the following; (however, it is impossible to form aSpiro bond due to the aromatic ring)

[0089] (a) a case of forming a condensed ring

[0090] (b) a case of direct bonding through a single bond

[0091] (c) a case of bonding via a linking group

[0092] (d) a case of bonding via a linking group having n electrons

[0093] However, in the case of (b) or (c), it is necessary that twoaromatic rings have planar structures.

[0094] Examples of condensed rings(condensed rings of at least twoaromatic rings) of (a) include an indene ring, a naphthalene ring, anazulene ring, a fluorene ring, a phenanthrene ring, an anthracene ring,an acenaphthylene ring, a biphenylene ring, a naphthacene ring, a pyrenering, an indole ring, an isoindole ring, a benzofuran ring, abenzothiophene ring, an indolizine ring, a benzoxazole ring, abenzothiazole ring, a benzimidazole ring, a benzotriazole ring, a purinering, an indazole ring, a chromene ring, a quinoline ring, anisoquinoline ring, a quinolidine ring, a quinazoline ring, a cinnolinering, a quinoxaline ring, a phthalazine ring, a pteridine ring, acarbazole ring, an acridine ring, a phenanthridine ring, a xanthenering, a phenazine ring, a phenothiazine ring, a phenoxathiin ring, aphenoxazine ring, and a thianthrene ring. Of these, preferred are anaphthalene ring, an azulene ring, an indole ring, a benzoxazole ring, abenzothiazole ring, a benzimidazole ring, a benzotriazole ring, and aquinoline ring.

[0095] The single bond of (b) is preferably a bond between carbon atomsof two aromatic rings. An aliphatic ring or a non-aromatic heterocyclicring may be formed between two aromatic rings by bonding two aromaticrings using at least two single bonds.

[0096] The linking group or π electron containing a linking group of (c)or (d) preferably bonds to the carbon atom of two aromatic rings. Thelinking group is preferably an alkylene group, an alkenylene group, analkynylene group, —Co—, —O—, —NH—, —S—, or combinations thereof.Examples of linking groups comprised of some combinations are describedbelow. The right and left relationship of the examples of linking groupsdescribed below may be reversed. Examples include —CO—O—, —CO—NH—,-alkylene-O—, —NH—CO—NH—, —NH—CO—O—, —O—CO—O—, —O-alkylene-O—,—CO-alkenylene-, —CO-alkenylene-NH—, —CO-alkenylene-O—,-alkylene-CO—O-alkylene-O—CO-alkylene-,—O-alkylene-CO—O-alkylene-O—CO-alkylene-O—, —O—CO-alkylene-CO—O—,—NH—CO-alkenylene-, and —O—CO-alkenylene. Particularly, —CO— andalkenylene are preferred as a group which directly bonds to an aromaticring or an aromatic heterocyclic ring.

[0097] Aromatic rings as well as linking groups may have substituent(s).However, it is required that the substituents do not result in astructure which results in no steric hindrance, but namely one whichresults in a planar structure. Types and positions of the substituentsresult in the steric hindrance. Of the types of substituents,dimensionally bulky substituents(e.g. a tertiary alkyl group) tend toresult in such steric hindrance. In regard to the positions ofsubstituents, it is preferable that a position adjacent to the bondbetween aromatic rings (in the case of a benzene ring, being an orthoposition) is avoided, since, when substituted, the aforesaid sterichindrance tends to occur.

[0098] Examples of substituents include a halogen atom (F, Cl, Br, andI), a hydroxyl group, a carboxyl group, a cyano group, an amino group, anitro group, a sulfo group, a carbamoyl group, a sulfamoyl group, aureido group, an alkyl group, an alkenyl group, an alkynyl group, analiphatic acyl group, an aliphatic acyloxy group, an alkoxyl group, analkoxycarbonyl group, an alkoxycarbonylamino group, an alkylthio group,an alkylsulfonyl group, an aliphatic amide group, an aliphaticsulfonamide group, an aliphatic substituted amino group, an aliphaticsubstituted carbamoyl group, an aliphatic substituted sulfamoyl group,an aliphatic substituted ureido group and a non-aromatic heterocyclicgroup.

[0099] The number of carbon atoms of an alkyl group is preferably 1 to8. A chain alkyl group is more preferable than a cyclic alkyl group, buta straight chain alkyl group is particularly preferred. The alkyl groupmay further have substituent(s) (e.g. a hydroxyl group, a carboxylgroup, an alkoxyl group, and an alkyl substituted amino group). Examplesof alkyl groups (including substituted alkyl groups) include a methylgroup, an ethyl group, an n-butyl group, an n-hexyl group, a2-hydroxyethyl group, a 4-carboxybutyl group, a 2-methoxyethyl group,and a 2-diethylaminoethyl group. The number of carbon atoms of thealkenyl group is preferably 2 to 8. A chain alkenyl group is morepreferable than a cyclic alkenyl group, but a straight chain alkenylgroup is particularly preferred. The alkenyl group may further havesubstituent(s). Examples of alkenyl groups include a vinyl group as wellas a 1-hexenyl group. The number of carbon atoms of the alkynyl group ispreferably 2 to 8. A chain alkynyl group is more preferable than acyclic alkynyl group, while a straight chain alkynyl group isparticularly preferred. The alkynyl group may further havesubstituent(s). Examples of alkynyl groups include an ethynyl group, a1-butynyl group, and a 1-hexynyl group.

[0100] The number of carbon atoms of the aliphatic acyl group ispreferably 1 to 10. Examples of aliphatic acyl groups include an acetylgroup, a propanoyl group, and a butanoyl group. The number of carbonatoms of the aliphatic acyloxy group is preferably 1 to 10. Examples ofthe aliphatic acyloxy group include an acetoxy group. The number ofcarbon atoms of the alkoxy group is preferably 1 to 8. The alkoxy groupmay further have substituent(s) (e.g. an alkoxyl group). Examples of thealkoxy groups (including an substituted alkoxy group) include a methoxygroup, an ethoxy group, a butoxy group, and a methoxyethoxy group. Thenumber of carbon atoms of the alkoxycarbonyl group is preferably 2 to10. Examples of alkoxycarbonyl groups include a methoxycarbonyl groupand an ethoxycarbonyl group. The number of carbon atoms of thealkoxycarbonylamino group is preferably 2 to 10. Examples ofalkoxycarbonylamino groups include a methoxycarbonylamino group and anethoxycarbonylamino group.

[0101] The number of carbon atoms of the alkylthio group is preferably 1to 12. Examples of alkylthio groups include a methylthio group, anethylthio group, and an octylthio group. The number of carbon atoms ofthe alkylsulfonyl group is preferably 1 to 8. Examples of alkylsulfonylgroups include a methanesulfonyl group and an ethanesulfonyl group. Thenumber of carbon atoms of the aliphatic amide group is preferably 1 to10. Examples of the aliphatic amide group include an acetamide group.The number of carbon atoms of the aliphatic sulfonamide group ispreferably 1 to 8. Examples of the aliphatic sulfonamide groups includea methanesulfonamide group, a butanesulfonamide group, and ann-octanesulfonamide group. The number of carbon atoms of the aliphaticsubstituted amino group is preferably 1 to 10. Examples of the aliphaticsubstituted amino groups include a dimethylamino group, a diethylaminogroup, and a 2-carboxyethylamino group. The number of carbon atoms ofthe aliphatic substituted carbamoyl group is preferably 2 to 10.Examples of the aliphatic substituted carbamoyl groups include amethylcarbamoyl group and a diethylcarbamoyl group. The number of carbonatoms of the aliphatic substituted sulfamoyl group is preferably 1 to 8.Examples of the aliphatic substituted sulfamoyl groups include amethylsulfamoyl group and a diethylsulfamoyl group. The number of carbonatoms of the aliphatic substituted ureido group is preferably 2 to 10.Examples of the aliphatic substituted ureido group include amethylureido group. Examples of the non-aromatic heterocyclic groupsinclude a piperidino group and a morpholino group.

[0102] The molecular weight of these compounds is preferably 300 to 800,while the boiling point is preferably 260° C. or higher. It is possibleto determine the boiling point employiong a commercially availablemeasurement apparatus (for example, TG/DTA100, manufactured by SeikoDenshi Kogyo Co.). Specific examples are shown below.

[0103] Further, other than those described above, preferably employed ascompounds which have at least two aromatic rings in accordance with thepresent invention and in which at least two aromatics rings result in aplanar structure are compounds having a triphenylene ring, representedby General Formula (1) described below.

[0104] In General Formula (1), each of R₁, R₂, R₃, R₄, and R₅independently is a hydrogen atom, a halogen atom, a nitro group, a sulfogroup, an aliphatic group, an aromatic group, a heterocyclic group,—O—R₁₁, —S—R₁₂, —CO—R₁₃, —O—CO—R₁₄, —CO—O—R₁₅, —O—CO—O—R₁₆, —BR₁₇R₁₈,—CONR₁₉R₂₀, —NR₂₁—CO—R₂₂, —O—Co—NR₂₃R₂₄, —SiR₂₅R₂₆R₂₇, —O—SiR₂₈R₂₉R₃₀,—S—CO—R₃₁, —OSO₂—R₃₂, —SO—R₃₃, —NR₃₄—CO—OR₃₅, —SO₂—R₃₆ or—R₃₇—CONR₃₈R₃₉, and each of R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆, R₁₇, R₁₈, R₁₉,R₂₀, R₂₁, R₂₂, R₂₃, R₂₄, R₂₅, R₂₆, R₂₇, R₂₈, R₂₉, R₃₀, R₃₁, R₃₂, R₃₃,R₃₄, R₃₅, R₃₆, R₃₇, R₃₈, and R₃₉ independently is independently ahydrogen atom, an aliphatic group, or a heterocyclic group. R₁ and R₂,R₃ and R₄, or R₅ and R₆ may be joined together to form a ring.

[0105] R₁, R₂, R₃, R₄, R₅, and R₆ are preferably —O—R₁₁, —S—R₁₂,—O—CO—R₁₄, —OCO—R₁₆, —NR₁₇R₁₈, —NR₂₁, —CO—R₂₂, or —O—CO—NR₂₃R₂₄, aremore preferably —O—R₁₁, —S—R₁₂, —O—CO—R₁₄, —OCO—O—R₁₆, or —O—CONR₂₃R₂₄,and are still more preferably —OR₁₁ or —O—CO—R₁₄, and are mostpreferably —O—CO—R₁₄.

[0106] R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆, R₁₇, R₁₈, R₁₉, R₂₀, R₂₁, R₂₂, R₂₃,R₂₄, R₂₅, R₂₆, R₂₇, R₂₈, R₂₉, R₃₀, R₃₁, R₃₂, R₃₃, R₃₄, R₃₅, R₃₆, R₃₇,R₃₈, and R₃₉ are preferably hydrogen atoms, aliphatic groups, oraromatic groups. R₁₄ of —CO—R₁₄ is most preferably an aromatic group.Further, in General Formula (1), R₁, R₂, R₃, R₄, R₅, and R₆ arepreferably the same group.

[0107] In the present invention, the aliphatic group refers to an alkylgroup, an alkenyl group, an alkynyl group, a substituted alkyl group, asubstituted alkenyl group, and a substituted alkynyl group. The alkylgroup may be a cyclic group (such as a cycloalkyl group). Further, thealkyl group may be branched. The number of carbon atoms of the alkylgroup is preferably 1 to 30, is more preferably 1 to 20, and is mostpreferably 1 to 10. Examples of alkyl groups include a methyl group, anethyl group, an i-propyl group, a butyl group, an i-butyl group, ans-butyl group, a t-pentyl group, a hexyl group, an octyl group, at-octyl group, a dodecyl group, and a tetracosyl group. The alkenylgroup may be a cyclic group (such as a cycloalkenyl group). Further, thealkenyl group may be branched. The alkenyl group may have two or moredouble bonds.

[0108] The number of carbon atoms of the alkenyl group is preferably 2to 30, is more preferably 2 to 20, and is most preferably 2 to 10.Examples of the alkenyl groups include a vinyl group, an allyl group,and a 3-heptenyl group. The alkynyl group may be a heterocyclic group(such as a cycloalkynyl group). Further, the alkynyl group may bebranched. The alkynyl group may have at least two triple bonds. Thenumber of carbon atoms of the alkynyl group is preferably 2 to 30, ismore preferably 2 to 20, and is most preferably 2 to 10. Examples ofalkynyl groups include an ethynyl group, a 2-prpynyl group, a 1-pentynylgroup and a 2,4-octadynyl group.

[0109] Examples of substituents of the substituted alkyl group, thesubstituted alkenyl group, and the substituted alkynyl group include ahalogen atom, a nitro group, a sulfo group, an aromatic group, aheterocyclic group, —O—R₄₁, —S—R₄₂, —CO—R₄₃, —O—CO—R₄₄, —CO—R₄₅,—O—CO—OR₄₆, —NR₄₇R₄₈, —CO—NR₄₉R₅₀, —NR₅₁, —CO—R₅₂, —O—CO—NR₅₃R₅₄,—SiR₅₅R₅₆R₅₇R₅₈, and —O—SiR₅₉R₆₀OR₆₁R₆₂. R₄₁, R₄₂, R₄₃, R₄₄, R₄₅, R₄₆,R₄₇, R₄₈, R₄₉, R₅₀, R₅₁, R₅₂, R₅₃, R₅₄, R₅₅, R₅₆, R₅₇, R₅₈, R₅₉, R₆₀,R₆₁, and R₆₂ are each independently a hydrogen atom, an aliphatic group,an aromatic group, or a heterocyclic group.

[0110] The alkyl portion of the substituted alkyl group is the same asthe aforesaid alkyl group. Examples of the substituted alkyl groupsinclude a benzyl group, a phenethyl group, a 2-methoxyethyl group, anethoxymethyl group, a 2-(2-methoxyethoxy)ethyl group, a 2-hydroxyethylgroup, a hydroxymethyl group, a 2-carboxyethyl group, a carboxymethylgroup, an ethoxycarbonylmethyl group, a 4-acryloyloxybutyl group, atrichloromethyl group, and a perfluoropentyl group. The alkenyl portionof the substituted alkenyl group is the same as the aforesaid alkenylgroup. Examples of the substituted alkynyl groups include a4-butoxyphenylethynyl group, a 4-propylphenylethynyl group, and atrimethylsilylethynyl group.

[0111] In the present invention, the aromatic group refers to an arylgroup and a substituted aryl group. The number of carbon atoms of thearyl group is preferably 6 to 30, is more preferably 6 to 30, and ismost preferably 6 to 10. Examples of the aryl groups include a phenylgroup, a 1-naphthyl group, and a 2-naphthyl group. Examples of thesubstituents of the substituted aryl group include a halogen atom, anitro group, a sulfonic acid group, an aliphatic group, an aromaticgroup, a heterocyclic group, —O—R₇₁, —S—R₇₂, —CO—R₇₃, —O—CO—R₇₄,—CO—O—R₇₅, —O—CO—O—R₇₆, —NR₇₇R₇₈, —CO—NR₇₉R₈₀, —NR₁₈—CO—R₈₂,—O—CO—NR₈₃R₈₄, —SiR₈₅R₈₆R₈₇R₈₈, and —O—SiR₈₉R₉₀R₉₁R₉₂.

[0112] Each of R₇₁, R₇₂, R₇₃, R₇₄, R₇₅, R₇₆, R₇₇, R₇₈, R₇₉, R₈₀, R₈₁,R₈₂, R₈₃, R₈₄, R₈₅, R₈₆, R₈₇, R₈₈, R₈₉, R₉₀, R₉₁, and R₉₂ independentlyis a hydrogen atom, an aliphatic group, an aromatic group, or aheterocyclic group.

[0113] The aryl portion of the substituted aryl group is the same as theaforesaid aryl group. Examples of substituted aryl groups include ap-biphenyl group, a 4-phenylethynylphenyl group, a 2-methoxyphenylgroup, a 3-methoxyphenyl group, a 4-methoxyphenyl group, a2-ethoxyphenyl group, a 3-ethoxyphenyl group, a 4-ethoxyphenyl group, a2-propoxyphenyl group, a 3-propoxyphenyl group, a 4-propoxyphenyl group,a 2-butoxyphenyl group, a 3-butoxyphenyl group, a 4-butoxyphenyl group,a 2-hexyloxyphenyl group, a 3-hexyloxyphenyl group, a 4-hexyloxyphenylgroup, a 2-octyloxyphenyl group, a 3-octyloxyphenyl group, a4-octyloxyphenyl group, a 2-dodecyloxyphenyl group, a 3-dodecyloxyphenylgroup, a 4-dodecyloxyphenyl group, a 2-tetracocyloxyphenyl group, a3-tetracocyloxyphenyl group, a 4-tetracocyloxyphenyl group, a3,4-dimethoxyphenyl group, a 3,4-diethoxyphenyl group, a3,4-dihexyloxyphenyl group, a 2,4-dimethoxyphenyl group, a2,4-diethoxyphenyl group, a 2,4-dihexyloxyphenyl group, a3,5-dimethopxyphenyl group, a 3,5-dimethoxyphenyl group, a3,5-dihexyloxyphenyl group, a 3,4,5-trimethoxyphenyl group, a3,4,5-triethoxyphenyl group, a 3,4,5-trihexyloxyphenyl group, a2,4,6-trimethoxyphenyl group, a 2,4,6-triethoxyphenyl group, a2,4,6-trihexyloxyphenyl group, a 2-fluorophenyl group, a 3-fluorophenylgroup, a 4-fluorophenyl group, a 2-chlorophenyl group, a 3-chlorophenylgroup, a 4-chlorophenyl group, a 2-bromophenyl group, a 3-bromophenylgroup, a 4-bromophenyl group, a 3,4-difluorophenyl group, a3,4-dichlorophenyl group, a 3,4-dibromophenyl group, a2,4-difluorophenyl group, a 2,4-dichlorophenyl group, a2,4-dibromophenyl group, a 3,5-difluorophenyl group, a3,5-dichlorophenyl group, a 3,5-dibromophenyl group, a3,4,5-trifluorophenyl group, a 3,4,5-trichlorophenyl group, a3,4,5-tribromophenyl group, a 2,4,6-trifluorophenyl group, a2,4,6-trichlorophenyl group, a 2,4,6-tribromophenyl group, apentafluorophenyl group, a pentachlorophenyl group, a pentabromophenylgroup, a 2-iodophenyl group, a 3-iodophenyl group, a 4-iodophenyl group,a 2-formylphenyl group, a 3-formylphenyl group, a 4-formylphenyl group,a 2-benzoylphenyl group, a 3-benzoylphenyl group, a 4-benzoylphenylgroup, a 2-carboxyphenyl group, a 4-carboxyphenyl group, an o-tolylgroup, a m-tolyl group, a p-tolyl group, a 2-ethylphenyl group, a3-ethylphenyl group, a 4-ethylphenyl group, a 2-(2-methoxyethoxy)phenylgroup, a 3-(2-methoxyethoxy)phenyl group, a 4-(2-methoxyethoxy)phenylgroup, a 2-ethoxycarbonylphenyl group, a 3-ethoxycarbonylphenyl group, a4-ethoxycarbonylphenyl group, a 2-benzoyloxyphenyl group, a3-benzoyloxyphenyl group, and a 4-benzoyloxyphenyl group.

[0114] Heterocyclic groups may have a substituent(s). The heterocyclicring of the heterocyclic groups is preferably a 5- or 6-membered ring.The heterocyclic ring of the heterocyclic groups may be subjected tocondensation with an aliphatic ring, an aromatic ring, or anotherheterocyclic ring. Examples of hetero atoms of the heterocyclic ringsinclude B, N, O, S, Se, and Te. Examples of heterocyclic groups includea pyrrolidine ring, a morpholine ring, a 2-bora-1,3-dioxolan ring, and a1,3-thiazolidine ring. Examples of unsaturated heterocyclic ringsinclude an imidazole ring, a thiazole ring, a benzothiazole ring, abenzoxazole ring, a benzotriazole ring, a benzoselenazole ring, apyridine ring, a pyrimidine ring and a quinoline ring. Examples ofsubstituents of the heterocyclic groups are the same as the examples ofsubstituents of the substituted aryl group.

[0115] The molecular weight of compounds having a triphenylene ring ispreferably 300 to 2,000, while the boiling point is preferably at least260° C. It is possible to determine the boiling point employing acommercially available measurement apparatus (for example, TG/DTA100,manufactured by Seiko Denshi Kogyo Co.). Shown below are specificexamples of R, corresponding to General Formula (2), described below, ofcompounds in which substituents of R₁ through R₆ of aforesaid GeneralFormula (1) comprise the six same triphenylene rings.

[0116] Listed as R may be (B-1)fluoro, (B-2) chloro, (B-3) bromo, (B-4)formyl, (B-5)benzoyl, (B-6)carboxyl, (B-7) butylamino, (B-8)benzylamino,(B-9)trimethylsilyloxy, (B-10) 1-pentynyl, (B-11)ethoxycarbonyl, (B-12)2-hydroxyethoxycarbonyl, (B-13)phenoxycarbonyl, (B-14)N-phenylcarbamoyl,(B-15)N,N-diethylcarbamoyl, (B-16) 4-methoxybenzoyloxy,(B-17)N-phenylcarbamoyloxy, (B-18) hexyloxy, (B-19)4-hexyloxybenzoyloxy, (B-20)ethoxy, (B-21) benzoyloxy, (B-22)m-dodecyloxyphenylthio, (B-23) t-octylthio, (B-24) p-fluorobenzoylthio,(B-25)isobutyrylthio, (B-26) p-methylbenzenesulfinyl,(B-27)ethansulfinyl, (B-28) benzenesulfonyl, (B-29)methanesulfonyl,(B-30) 2-methoxyethoxy, (B-31)propoxy, (B-32) 2-hydroxyethoxy, (B-33)2-carboxyethoxy, (B-34) 3-heptenyloxy, (B-35) 2-phenylethoxy,(B-36)trichloromethoxy, (B-37) 2-propinyloxy, (B-38) 2,4-octadynylpoxy,(B-39)perfluoropentyloxy, (B-40) ethoxycarbonylmethoxy, (B-41)p-methoxyphenoxy, (B-42) m-ethoxyphenoxy, (B-43) o-chlorophenoxy, (B-44)m-dodecyloxyphenoxy, (B-45) 4-pyridyloxy, (B-46) pentafluorobenzoyloxy,(B-47) p-hexyloxybenzoyloxy, (B-48) 1-naphthoyloxy, (B-49)2-naphthoyloxy, (B-50) 5-imidazolecarbonyloxy, (B-51)o-phenoxycarbonylbenzoyloxy, (B-52) m-(2-methoxyethoxy)benzoyloxy,(B-53) o-carboxybenzoyloxy, (B-54) p-formylbenzoyloxy, (B-55)m-ethoxycarbonylbenzoyloxy, (B-56) p-pyvaroylbenzoyloxy, (B-57)propionyloxy, (B-58)phenylacetoxy, (B-59) cinnamoyloxy,(B-60)hydroxyacetoxy, (B-61)ethoxycarbonylacetoxy, (B-62)m-butoxyphenylpropioroyloxy, (B-63)propioroyloxy, (B-64)trimethylsilylpropioloyloxy, (B-65) 4-octenoyloxy, (B-66)3-hydroxypropionyloxy, (B-67) 2-methoxyethoxyacetoxy, (B-68)perfluorobutylyloxy, (B-69)methanesulfonyloxy, (B-70)p-toluenesulfonyloxy, (B-71)triethylsilyl, (B-72)m-butoxyphenoxycarbonylamino, (B-73)hexyl, (B-74)phenyl, (B-75)4-pyridyl, (B-76)benzyloxycarbonyloxy, (B-77) m-chlorobenzamide, and(B-78) 4-methylanilino.

[0117] Shown below are specific examples of R corresponding to GeneralFormula (3), described below, of the compounds in which of substituentsof R₁ through R₆ in aforesaid General Formula (1), five substituents arehydrogen atoms and the remaining substituent is the same triphenylenering of R.

[0118] Listed as R may be (B-79)nitro, (B-80)sulfo, (B-81) formyl,(B-82)carboxyl, (B-83)methoxycarbonyl, (B-84) benzyloxycarbonyl, and(B-85)phenoxycarbonyl.

[0119] Shown below are specific examples of R corresponding to GeneralFormula (4) of compounds in which R₁ of aforesaid General Formula (1) isa hydroxyl group and the five substitutes of R₂ through R₆ are the sametriphenylene rings of R.

[0120] Listed as R may be (B-86) butoxy, (B-87)hexyloxy, (B—88)dodecyloxy, (B-89)hexanoyloxy, and (B-90) carboxymethoxy.

[0121] Further, listed as other examples of R₁ through R₆ of aforesaidGeneral Formula (1) may be B-91 through B-100 described below.

[0122] From the viewpoint of minimizing bleed-out, the added amount ofcompounds which have at least two aromatic rings and in which at leasttwo aromatic rings exhibit a planar structure to a cellulose ester dopeis preferably 0.4 to 10 percent by weight, and is more preferably 1.5 to10 percent by weight. The proportion of the aforesaid compounds in thecellulose ester film is preferably 0.01 to 20 parts by weight withrespect to 100 parts by weight of cellulose ester, is more preferably 5to 30 parts by weight, and is most preferably 8 to 30 parts by weight.

[0123] In order to minimize degradation of the cellulose ester film, itis preferable that degradation inhibitors such as antioxidants orradical scavengers are incorporated into the aforesaid cellulose esterfilm.

[0124] Preferably employed as the aforesaid degradation inhibitors arehindered phenol based compounds, which include 2,6-di-t-butyl-p-cresol,pentaerythrityl-tetrakisl[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],triethylene glycol-bis[3-t-butyl-5-methyl-4-hydroxyphenyl]propionate],1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine,2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,N,N′-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamide),1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, andtris-(3,5-di-t-butyl-4-hydroxybenzyl)-isocyanurate. Of these,2,6-di-t-butyl-p-cresol,pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,and triethyleneglycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate areparticularly preferred. Further, for example, hydrazine based metaldeactivating agents such asN,N′-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine andphosphorous based process stabilizers such astris(2,4-di-t-butylphenyl)phosphite may be simultaneously employed. Theadded amount of these compounds is preferably 1 ppm to 1.0 percent interms of weight ratio and is more preferably 10 to 10,000 ppm.

[0125] In order to minimize degradation of cellulose ester film due toultraviolet radiation, other than the aforesaid degradation minimizingagents, it is preferable that UV absorbers which function to eliminateor decrease ultraviolet radiation are incorporated. Preferred UVabsorbers are those which efficiently absorb ultraviolet radiationhaving a wavelength of 370 nm or shorter, and from the viewpoint ofvisibility of liquid crystal display, absorb minimal visible lighthaving a wavelength of 400 nm or longer. Examples includeoxybenzophenone based compounds, benzotriazole based compounds,salicylic acid ester based compounds, benzophenone based compounds,cyanoacrylate based compounds, and nickel complex based compounds.Particularly preferred UV absorbers are benzotriazole based compoundsand benzophenone based compounds. Of these, benzotriazole basedcompounds are preferred since they minimize unnecessary coloration ofcellulose ester. For example, Tinuvin 109, Tinuvin 171, Tinuvin 326,Tinuvin 327, and Tinuvin 328, manufactured by Ciba Specialty ChemicalsCo. may be preferably employed. However, depending on the used amount,low-molecular UV absorbers may deposit in the web or sublime duringcasting in the same manner as plasticizers. Consequently, the addedamount is 0.01 to 5 percent by weight with respect to cellulose ester,and is preferably 0.13-3 percent by weight. Incidentally, these UVabsorbers overlap the function of the compounds useful for the presentinvention, which have at least two aromatic rings and in which at leasttwo aromatic rings exhibit a planar structure.

[0126] It is preferable that minute particles are incorporated intocellulose ester film. It is preferable to incorporate minute inorganicparticles comprised of, for example, silicon dioxide, titanium dioxide,aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc,sintered calcium silicate, and calcium phosphate, and minute crosslinkedpolymer particles. Of these, silicon dioxide is preferred since it ispossible to minimize the haze of film. The average secondary particlesdiameter of the aforesaid minute particles is customarily 0.01 to 1.0μm. Their content is preferably 0.005 to 0.3 percent by weight withrespect to the cellulose ester. Minute particles comprised of silicondioxide are often subjected to a surface treatment employing organicsubstances. Such particles are preferred since it is possible todecrease the haze of film. Listed as organic substances which arepreferable for the surface treatment are halosilanes, alkoxysilanes(specifically, alkoxysilanes having a methyl group), silazane, andsiloxane. As the average diameter of minute particles increases, theresulting matting effect increases. On the contrary, as the averagediameter decreases, transparency increases. Consequently, the averageprimary particle diameter of the minute particles is preferably 5 to 50nm, and is more preferably 7 to 16 nm. These minute particles commonlyexist in cellulose ester film in the form of aggregates. As a result, itis preferable that a roughness of 0.01 to 1.0 μm be formed on thesurface of cellulose ester film. Listed as minute particles comprised ofsilicon dioxide may be Aerosil 200, 200V, 300, R972, R972V, R974, R202,R812, OX50, and TT600, manufactured by Aerosil Co. Of these, preferredare Aerosil 200V, R972, R972V, R974, R202, and R812. These minuteparticles may be employed in combinations of at least two types. When atleast two types are employed in combination, they may be used whilemixed at an optional ratio. In such a case, minute particles whichdiffer in average particle diameter and material, for example, Aerosil200V and R972 may be employed in the range of 0.1:99.9 to 99.9:0.1 interms of weight ratio. In the present invention, during preparation of adope, the minute particles may be mixed with cellulose ester, otheradditives, as well as organic solvents and then dispersed. However, itis preferable that being separated from the preparation of a celluloseester solution, minute particles are sufficiently dispersed to form adispersion and a dope is prepared. In order to disperse the aforesaidminute particles, it is preferable that minute particles are previouslyimmersed in organic solvents and the resulting mixture finely dispersedemploying a high shearing force homogenizer (such as a high pressurehomogenizer). Thereafter, it is preferable that the resulting dispersionis dispersed in a large amount of organic solvents, and the resultingdispersion is allowed to join with a cellulose ester solution, and mixedby an in-line mixer to prepare a dope. In that case, UV absorbers may beadded to the minute particle dispersion to form a liquid UV absorbercomposition.

[0127] The aforesaid degradation minimizing agents, UV absorbers and/orminute particles may be added together with cellulose ester and solventsduring preparation of the cellulose ester solution, or they may be addedduring or after preparation of the solution.

[0128] Organic solvents which are useful for preparation of the dopeaccording to the present invention may be employed without anylimitations as long as they are capable of simultaneously dissolvingcellulose ester, compounds which have at least two aromatic rings and inwhich at least two aromatic rings exhibit a planar structure. Listed asa chlorine based solvent may be, for example, methylene chloride, whilelisted as non-chlorine based solvents may be methyl acetate, ethylacetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolan,1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol,2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol,1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol,1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, andnitroethane. Of these, preferably employed are methylene chloride,methyl acetate, ethyl acetate, and acetone, however methyl acetate isparticularly preferred.

[0129] It is preferable that other than the aforesaid organic solvents,alcohols having 1 to 4 carbon atoms are incorporated into a dope in anamount of 1 to 40 percent by weight. When the alcohol ratio in the dopeincreases, the web becomes gel, resulting in ease of its peeling from ametal support. Further, when the alcohol ratio is low, dissolution ofcellulose ester in a non-chlorine based organic solvent system ispromoted. Listed as alcohols having 1 to 4 carbon atoms may be methanol,ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, andtert-butanol. Of these, ethanol is preferred due to dope stability,relatively low boiling point, desired drying property, and non-toxicity.

[0130] In order to achieve the desired surface quality of film, theconcentration of cellulose ester in a dope is preferably 15 to 40percent by weight, and dope viscosity is preferably controlled between100 to 500 poise (P).

[0131] Plasticizers may be added to the dope. Preferably employed asplasticizers may be phosphoric acid based plasticizers, phthalic acidester based plasticizers, glycolate based plasticizers, and citric acidester based plasticizers. Listed as phosphoric acid ester basedplasticizers may be the aforesaid triphenyl phosphate (TPP), tricresylphosphate, cresyl phenyl phosphate, octyl diphenyl phosphate, diphenylbiphenyl phosphate, trioctyl phosphate, and tributyl phosphate; listedas phthalic acid ester based plasticizers may be diethyl phthalate,dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutylphthalate, di-2-ethyl hexyl phthalate, butyl benzyl phthalate,di-2-ethylhexyl phthalate, butyl benzyl phthalate, and dibenzylphthalate; listed as citric acid esters may be acetyl trimethyl citrate,and acetyl tributyl citrate; listed as glycolate based plasticizers maybe alkyl phthalyl alkyl glycolate; and listed as others may be butyloleate, methyl acetyl ricinolate, dibutyl sebacate, and triacetin. Inthe present invention, glycolate based plasticizers may be preferablyemployed and it is possible to list alkyl phthalyl alkyl glycolates inwhich the alkyl group has 1 to 8 carbon atoms. Listed as preferredglycolate based plasticizers may be methyl phthalyl methyl glycolate,ethyl phthalyl ethyl glycolate (EPEG), propyl phthalyl propyl glycolate,butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methylphthalyl ethyl glycolate, ethyl phthalyl methyl glycolate, ethylphthalyl propyl glycolate, propyl phthalyl ethyl glycolate, methylphthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethylphthalyl butyl glycolate, butyl phthalyl methyl glycolate, butylphthalyl ethyl glycolate, propyl phthalyl butyl glycolate, butylphthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethylphthalyl octyl glycolate, octyl phthalyl methyl glycolate, and octylphthalyl ethyl glycolate. Of these, preferred are methyl phthalyl methylglycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propylglycolate, butyl phthalyl butyl glycolate, and octyl phthalyl octylglycolate. Of these, ethyl phthalyl ethyl glycolate is most preferablyemployed. Further, at least two types of these alkyl phthalyl alkylglycolates may be mixed and employed.

[0132] From the viewpoint of increasing a close contact force andminimizing bleeding-out from the film, the added amount of alkylphthalyl alkyl glycolates is preferably 1 to 10 percent by weight withrespect to the cellulose ester. Plasticizers other than those describedabove may be mixed with alkyl phthalyl alkyl glycolates.

[0133] (Optically Anisotropic Layer)

[0134] It is possible to form an optically anisotropic layer by applyinga liquid crystal composition (a liquid coating composition) comprisingrod-like liquid crystal compounds, the polymerization initiatorsdescribed below, and optional additives (for example, plasticizers,monomers, surface active agents, cellulose ester, 1,3,5-triazinecompounds, and chiral agents) onto an orientation layer, andsubsequently fixing the orientation of the aforesaid liquid crystalcompounds.

[0135] Preferably employed as rod-like liquid crystal compounds inaccordance with the present invention are azomethines, azoxys,cyanobiphenyls, cyanophenyl esters, benzoic acid esters,cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes,cyano-substituted phenylpyrimidines, alkoxy-substitutedphenylpyrimidines, phenyldioxanes, tolans, andalkenylcyclohexylbenzonitriles. Incidentally, metal complexes areincluded in the rod-like liquid crystal compounds. Further, employed asa rod-like liquid crystal compound may be liquid crystal polymerscomprising rod-like liquid crystal compounds in repeating units. Inother words, rod-like liquid crystal compounds may be joined to (liquidcrystal) polymers. Rod-like liquid crystal compounds are described inChapters 4, 7, and 11 of Kikan Kagaku Sosetsu (Quarterly ChemicalReview) Volume 22 Ekisho no Kagaku (Chemistry of Liquid Crystals)(1994), edited by Nihon Kagaku Kai, as well as in Chapter 3 of EkishoDevice Handbook (Handbook of Liquid Crystal Devices), edited by NihonGakujutsu Shinko Kai No. 142 Iinkai. The birefringence of rod-likeliquid crystal compounds is preferably in the range of 0.001 to 0.7. Itis preferable that rod-like liquid crystal compounds have polymerizablegroup(s) in order to fix the resulting orientation state. Examples ofpolymerizable groups (Q) are shown below.

[0136] Polymerizable groups (Q) are preferably polymerizable unsaturatedgroups (Q1-Q7), an epoxy group (Q8), or an aziridinyl group (Q9), andare more preferably polymerizable unsaturated groups, are mostpreferably polymerizable ethylenic unsaturated groups (Q1 to Q6). It ispreferable that rod-like liquid crystal compounds have a molecularstructure in which symmetry is held with respect to the short axisdirection. In order to achieve such a structure, it is preferable thatpolymerizable groups are positioned at both ends of the rod-likestructure. Examples of rod-like liquid crystal compounds are shownbelow.

[0137] On the other hand, listed as examples of the use of discoticliquid crystal compounds may be benzene derivatives described in theresearch report of C. Destrade et al., Mol. Cryst., Volume 71, page 111(1981), truxene derivatives described in the research reports of C.Destrade et al., Mol. Cryst., Volume 122, page 141 (1985) and PhysicsLett, A, Volume 78, page 82 (1990), cyclohexane derivatives described inthe research report of B. Kohne et al., Angew. Chem., Volume 96, page 70(1984); and azacrown based and phenylacetylene based macrocycles in theresearch reports of M. Lehn et al., J. Chem. Commun., page 1794 (1985)and J. Zhang et al., J. Am. Chem. Soc., Volume 116, page 2655 (1994).Further, discotic liquid crystal compounds include those having astructure in which the aforesaid compounds are generally used as amother nucleus at the center of the molecule and straight chain alkylgroups and alkoxy groups, and substituted benzoyloxy groups areradiately substituted while forming a straight chain, and the resultingcompounds exhibit liquid crystal properties. However, discotic liquidcrystal compounds are not limited to these as long as molecules exhibitnegative uniaxial property and definite orientation can be provided.Further, in the present invention, in an optically anisotropic layerformed employing discotic liquid crystal compounds, finally formed onesneed not to be the aforesaid compounds. For example, those which havelost crystal properties are included in which low molecular discoticliquid crystal compounds having a group(s) which undergoes reactionunder an application of heat or light, result in polymerization orcrosslinking via thermal or photolytic reaction. Preferable examples ofdiscotic liquid crystal compounds are described in Japanese PatentPublication Open to Public Inspection No. 8-5020. Further,polymerization of discotic liquid crystal compounds is described inJapanese Patent Publication Open to Public Inspection No. 8-27284.

[0138] In order to securely fix the discotic liquid crystal compounds bypolymerization, it is required that a polymerizable group(s) be joinedto the discotic core of discotic liquid crystal compounds as asubstituent. However, when the polymerizable group is directly joined tothe discotic core, it becomes difficult to maintain the desiredorientation state during polymerization reaction. Consequently, alinking group is introduced between the discotic core and thepolymerizable group. Therefore, discotic liquid crystal compounds havinga polymerizable group(s) are preferably those represented by GeneralFormula (5), described below.

[0139] General Formula (5) D(-L-P)_(n),

[0140] In General Formula (5), D represents a discotic core, Lrepresents a divalent linking group, P represents a polymerizable group,while n represents an integer of 4 to 12. Examples of the discotic core(D) are shown below. In each of the following examples, LP (or PL)refers to the combinations of the divalent linking group (L) and thepolymerizable group (P).

[0141] In General Formula (5), the divalent linking group (L) ispreferably an alkylene group, an alkenylene group, an arylene group,—C—, —NH—, —O—, and —S—, and a divalent linking group selected from thegroup consisting of combinations thereof. Divalent linking group (L) ismore preferably a divalent linking group prepared by combining at leasttwo divalent-groups selected from the group consisting of an alkylenegroup, an arylene group, —CO—, —NH—, —O—, and —S—. Divalent linkinggroup (L) is most preferably a divalent linking group which is formed bycombining at least two divalent groups selected from the groupconsisting of —CO— and —O—. The number of carbon atoms of the alkylenegroup is preferably 1 to 12. The number of carbon atoms of thealkenylene group is preferably 2 to 12. The number of carbon atoms ofthe arylene group is preferably 6 to 10.

[0142] Examples of divalent linking groups (L) are shown below. The leftside is joined to the discotic core (D), while the right side is joinedto the polymerizable group (P). AL represents an alkylene group or analkenylene group, while AR represents an arylene group. Incidentally,the alkylene group, alkenylene group and arylene group may have asubstituent (e.g. an alkyl group).

[0143] L1: -AL-CO—O-AL-

[0144] L2: -AL-CO—O-AL-O—

[0145] L3: -AL-CO—O-AL-O-AL-

[0146] L4: -AL-CO—O-AL-O—CO—

[0147] L5: —CO-AR-O-AL-

[0148] L6: —CO-AR-O-AL-O—

[0149] L7: —CO-AR-O-AL-O—CO—

[0150] L8: —CO—NH—Al—

[0151] L9: —NH-AL-C—

[0152] L10: —NH-AL-O—CO—

[0153] L11: —O-AL-

[0154] L12: —O-AL-C—

[0155] L13: —O-AL-O—CO—

[0156] L14: —O-AL-O—CO—NH-AL-

[0157] L15: —O-AL-S-AL-

[0158] L16: —O—CO-AR-O-AL-CO—

[0159] L17: —O—CO-AR-O-AL-O—CO—

[0160] L18: —O—CO-AR-O-AL-O-AL-O—CO—

[0161] L19: —O—CO-AR-O-AL-O-AL-O-AL-O—CO—

[0162] L20: —S-AL-

[0163] L21: —S-AL-O—

[0164] L22: —S-AL-C—CO—

[0165] L23: —S-AL-S—Al—

[0166] L24: —S-AR-AL-

[0167] Polymerizable group (P) of General Formula (5) is determinedbased on the type of polymerization reaction. Examples of polymerizablegroups (P) are shown below.

[0168] The polymerizable group (P) is preferably a polymerizableunsaturated group (P1, P2, P3, P7, P8, P15, P16 or P17) or an epoxygroup (P6 or P18), is more preferably a polymerizable unsaturated group,and is most preferably a polymerizable ethylenic unsaturated group (P1,P7, P8, P16, or P17). In General Formula (5), n is an integer of 4 to12. The specific figure is determined based on the type of the discoticcore (D). When a plurality of L and P is combined, they may be differentor the same.

[0169] When discotic liquid crystal compounds are employed, it ispreferable that the optically anisotropic layer exhibits negativebirefringence, the plane of discotic structure units is inclined to theplane of the cellulose ester film, and the angle between the plane ofthe discotic structure units and the surface of the cellulose ester filmvaries in depth of the optically anisotropic layer.

[0170] The angle of the plane of discotic structure units (theinclination angle) generally increases or decreases in depth of theoptically anisotropic layer as the distance from the bottom surface ofthe optically anisotropic layer increases. It is preferable that theinclination angle increases as the distance increases. Further, listedas the variation of the inclination angle may be a continuous increase,a continuous decrease, an intermittent increase, an intermittentdecrease, variation including a continuous increase and a continuousdecrease, and intermittent variation including an increase and adecrease. The intermittent variation includes the range in which theinclination angle does not vary on the way of the depth. The inclinationangle, even though including the range of no variation of theinclination angle, is totally increased or decreased. Further, it ispreferable that the inclination angle is totally increased andparticularly varies continuously.

[0171] It is generally possible to regulate the inclination angle ofdiscotic units on the support side by selecting discotic liquid crystalcompounds or materials of the orientation layer, or selecting rubbingmethods. Further, it is generally possible to regulate the inclinationangle of discotic units on the surface side (the ambient air side) byselecting discotic liquid crystal compounds or other compounds used withthe discotic liquid crystal compounds. Listed as examples of compoundsusable with discotic liquid crystal compounds may be plasticizers,surface active agents, as well as polymerizable monomers and polymers.It is possible to regulate the degree of variation of the inclinationangle, employing the same selection parameters as above.

[0172] Employed as plasticizers, surface active agents, andpolymerizable monomers may be any appropriate compounds as long as theyexhibit compatibility with discotic liquid crystal compounds, and enablevariation of the inclination angle of discotic liquid crystal compoundsor do not hinder their orientation. Of these, preferred arepolymerizable monomers (for example, compounds having a vinyl group, avinyloxy group, an acryloyl group, and a methacryloyl group). The addedamount of the aforesaid compounds is customarily 1-50 percent by weightwith respect to the discotic compounds, and is preferably 5 to 30percent by weight.

[0173] Employed as polymers which are used together with discotic liquidcrystal compounds may be any polymers as long as they exhibitcompatibility with discotic liquid crystal compounds and enablevariation of the inclination angle of discotic liquid crystal compounds.Listed as an example of the polymer may be cellulose ester. Listed aspreferable examples of cellulose ester may be cellulose acetate,cellulose acetate propionate, hydroxypropyl cellulose, and celluloseacetate butyrate. The added amount of the aforesaid polymers iscustomarily 0.1 to 10 percent by weight with respect to the discoticliquid crystal compounds so that they do not hinder the orientation ofthe discotic liquid crystal compounds, is more preferably 0.1 to 8percent by weight, and is still more preferably 0.1 to 5 percent byweight.

[0174] An optically anisotropic layer is prepared in such a manner thata solution prepared by dissolving discotic liquid crystal compounds andother compounds in solvents is applied onto an orientation layer, dried,subsequently heated to a discotic nematic phase forming temperature, andthen cooled while maintaining an orientation state (a discotic nematicphase). Alternatively, the aforesaid optically anisotropic layer isprepared in such a manner that a solution, prepared by dissolvingdiscotic liquid crystal compounds and other compounds (for example,polymerizable monomers and photopolymerization initiators) in solvents,is applied onto an orientation layer, dried, subsequently heated to adiscotic nematic phase forming temperature followed by polymerization byexposure to ultraviolet radiation, and further cooled. The discoticnematic liquid crystal phase-solid phase transition temperature range ispreferably 70 to 300° C., and is most preferably 70 to 170° C.

EXAMPLES

[0175] The embodiments and effects of the present invention will now bedescribed.

[0176] Initially, all the measurement methods of various physicalproperties will be described below.

[0177] (Measurement of Degree of Substitution and Degree of Acetylationof Cellulose Ester Film)

[0178] Degree of acetyl substitution (DSa) and degree of propionylsubstitution (DSp) were determined in accordance with ASTM-D817-96.Degree of substitution (DSa), as described herein, refers to the valuerepresented by a glucopyranose unit which relates to the number of OHgroups in a cellulose ester molecule, which is or are substituted whilereacting with acetic acid. Consequently, DSa ranges from 0 to 3.

[0179] Further, the degree of acetylation refers to the percent byweight of acetic acid in cellulose acetate and is calculated based onthe formula described below.

[0180] Degree of acetylation ={DSa×(molecular weight ofCH₃COOH)}/{(molecular weight of (C₆H₁₀O₅)+DSa×(molecular weight ofCH₂CO)+DSp×(molecular weight of CH₃CHCO)}(R₀, R_(t), Delayed-Phase AxisDirection)

[0181] The average refractive index of samples was determined employingan Abbe's refractometer. Further, the birefringence index was determinedat a wavelength of 590 nm under an ambience of 23° C. and 55 percentrelative humidity, employing an automatic birefringence analyzerKOBRA-21ADH (manufactured by Oji Scientific Instruments). Subsequently,refractive indices N_(x), N_(y), and N_(z) were obtained throughcalculation utilizing the determined values of the phase difference andaverage refractive indices. Simultaneously, the delayed-phase axisdirection was also determined.

[0182] (Measurement of Photoelastic Coefficients C(md) and C(td))

[0183] After casting and drying, retardation (R) within a film plane wasdetermined while applying a load to the film, and subsequently, Δn(=R/d) was obtained by dividing the resulting retardation by filmthickness (d). While varying the applied load, Δn was determined and aweight-Δn curve was prepared. The resulting gradient was designated as aphotoelastic coefficient. Retardation (R) within the film plane wasdetermined at a wavelength of 589 nm, under an ambience of 23° C. and 55percent relative humidity, employing a retardation measurement apparatus(KOBURA31PR, manufactured by Oji Scientific Instruments). A load wasapplied in the md and td directions of the film and the resultingphotoelastic coefficients were designated as C(md) Pa⁻¹ and C(td) Pa⁻¹,respectively.

[0184] (Dimensional Variation Ratio)

[0185] Parallel lines at a spacing of about 10 cm were marked on a filmemploying a cutter, and the film was allowed to stand for 24 hours at23° C. and 50 percent relative humidity. The resulting spacing was thenmeasured. Thereafter, the film was stored for 50 hours at 80° C. and 90percent relative humidity, followed by storing the film for at least 24hours at 23° C. and 50 percent relative humidity, and the resultingdistance was again measured.

[0186] Dimensional variation ratios S(md) and S(td) in the md and tddirections were determined based on spacing variation prior to and afterstorage.

[0187] (Viewing Angle Characteristics and Durability)

[0188] In order to evaluate viewing angle characteristics, the amount oftransmitted light was determined on a black display as well as on awhite display, employing an EZ-Contrast, manufactured by ELDIM Ltd.Viewing angle characteristic were evaluated while calculating contrast=(the amount of transmitted light on a white display)/the amount oftransmitted light on a black display).

[0189] In order to evaluate the durability of viewing angle functions,viewing angle characteristics were determined prior to after storage at60° C. and 90 percent relative humidity for 500 hours, and the variationof the angle showing a viewing angle of contrast 10 was observed.

[0190] Evaluation

[0191] A: no viewing angle variation neither in the mechanical directionnor in the transverse direction

[0192] B: the viewing angle varied 2 to 5 degrees either in themechanical direction or in the transverse direction

[0193] C: the viewing angle varied 2 to 5 degrees either in themechanical direction or in the transverse direction

[0194] In this case, evaluations A and B are commercially viable.

Example 1

[0195] (Preparation of Dope A)

[0196] One part by weight of Aerosil R972 and 9 parts by weight ofethanol were blended in a vessel, and the resulting mixture was finelydispersed employing a Manton-Gaulin homogenizer with a shearing force of30 MPa to prepare a minute particle stock composition. Subsequently, theresulting stock composition was diluted by 9 parts by weight ofmethylene chloride in a pressure proof sealed vessel, and the resultingmixture was designated as a filler dispersion diluted liquidcomposition.

[0197] Dissolved in 14.2 parts by weight of methylene chloride were 1.2parts by weight of a UV absorber and 0.7 part by weight of celluloseester (described in A of Table 1), and 3.0 parts by weight of theaforesaid filler dispersion diluted liquid composition was added whilestirring. The resulting mixture was designated as a filler additionliquid composition. The cellulose ester solution composition describedbelow was introduced into another pressure proof sealed vessel, wherebya cellulose ester solution was prepared employing a high temperaturedissolution method. During that time, pressure in the pressure proofsealed vessel was maintained at 0.2 MPa and dissolution was carried outwhile stirring. Subsequently, 0.04 part by weight of the aforesaidfiller addition liquid composition was poured into 1.0 part by weight ofa cellulose ester solution and after being well stirred, the resultingmixture was allowed to stand overnight. Thereafter, the resultingsolution was filtered employing an Azumi Filter Paper No. 244,manufactured by Azumi Filter Paper Co., whereby Dope A was prepared.TABLE 1 Cellulose Degree of Ester X Y X + Y Acetylation A 1.9 0.75 2.6540% B 2.8 0 2.8 60%

[0198] (Cellulose Ester Solution Composition) Cellulose ester (describedin  100 weight parts A of Table 1) TPP  8.5 weight parts EPEG   2 weightparts Methylene chloride  300 weight parts Ethanol   57 weight parts

[0199] (Preparation of Dope B)

[0200] Dope B was prepared in the same manner as Dope A, except thatcellulose ester (described in A of Table 1) was replaced with CelluloseEster B at a degree of acetylation of 60 percent and 6 parts by weightof the aforesaid Exemplified Compound A-7 were added to 100 parts byweight of cellulose ester.

[0201] (Preparation of Dope C)

[0202] Dope C was prepared in the same manner as Dope B, except thatCompound A-7 was omitted.

[0203] (Preparation of Optical Compensation Cellulose Ester Film)

[0204] Aforesaid Dope A, maintained at 35° C., was extruded from a dieonto a stainless steel support belt maintained at 35° C. The drying airtemperature onto the support was maintained at 40° C. Thereafter, thesupport temperature was lowered to 20° C., and the resulting web waspeeled from the support at a residual solvent amount of 80 percent byweight. Subsequently, while both edges of the web were maintainedemploying a tenter, orientation was carried out under conditions of anorientation factor of 1.3, a web temperature of 80° C. duringorientation, and a residual web solvent ratio of 20 percent duringorientation. The resulting web was dried employing 500 rollers at aconveying tension of 100 N and a drying temperature of 100° C., whileperforming relaxation in the transverse direction, whereby OpticalCompensation Cellulose Ester Film D was prepared in the form of a woundroll.

[0205] (Preparation of Viewing Angle Compensation Integral TypePolarizing Plate (Optical Compensation Polarizing Plate))

[0206] Rolled Optical Compensation Cellulose Ester Film D was treated at60° C. in a 2 mol/l aqueous sodium hydroxide solution for 2 minutes.After water washing, the resulting film was dried at 100° C. for 10minutes, whereby an alkali saponificated polarizing plate protectivefilm was prepared.

[0207] On the other hand, a 120 μm thick polyvinyl alcohol film wasimmersed in 100 parts by weight of an aqueous solution comprising onepart by weight of iodine and 4 parts by weight of boric acid, and theresulting film was oriented at 50° C. by a factor of 4, whereby apolarizer (a polarizing film) was prepared.

[0208] Polarizing plate protective film was adhered to both sides of thepolarizer employing a 5 percent aqueous completely saponificated typepolyvinyl alcohol solution as an adhesive. At this time, adhesion wascarried out so that the transmission axis of the polarizer and thedelayed-phase axis of the optical compensation cellulose ester film wereparallel.

[0209] Further, rolled Optical Compensation Cellulose Ester Film F (acomparative example) was prepared in the same manner as rolled OpticalCompensation Cellulose Ester Film D, except that the resulting film wasdried without relaxing the film after orientation in the transversedirection.

[0210] The resulting film was adhered to the polarizer employing thesame method as above and Viewing Angle Compensation Integral TypePolarizing Plate G (being a comparative example) was prepared.

[0211] Optical Compensation Cellulose Ester Film H, which had beensubjected to relaxing while drying, was prepared in the same manner asrolled Optical Compensation Cellulose Ester Film D, except that Dope Awas replaced with Dope B.

[0212] Rolled Optical Compensation Cellulose Ester Film I (a comparativeexample) was prepared in the same manner as rolled Optical CompensationCellulose Ester Film F, except that Dope A was replaced with Dope B.

[0213] By employing the resulting Films H and I, Viewing AngleCompensation Integral Type Polarizing Plates M (present invention) and N(comparative example) were prepared and evaluated.

[0214] Further, by employing Dope C, prepared was Optical CompensationCellulose Ester Film J which had been subjected to relaxation drying. Byemploying the resulting Film J, Viewing Angle Compensation Integral TypePolarizing Plate K (the present invention) was prepared and evaluated.

[0215] In Table 2 below, physical properties of viewing anglecompensation ester films as well as the performance of opticalcompensation polarizing plates employing the same are summarized andshown. TABLE 2 Durability of Polarizing Viewing Angle Plate R₀ R_(t)C(md) C(td) |S(md)| |S(td)| C(md) × |S(md)| C(td) × |S(td)| Function E35 135 1.26 × 10⁻¹¹ 1.40 × 10⁻¹¹ 0.009 0.003 1.1 × 10⁻¹³ > 4.2 × 10⁻¹⁴ AG 38 138 1.26 × 10⁻¹¹ 1.38 × 10⁻¹¹ 0.002 0.008 2.5 × 10⁻¹⁴ < 1.1 × 10⁻¹³C M 40 140 1.26 × 10⁻¹¹ 1.31 × 10⁻¹¹ 0.002 0.001 2.5 × 10⁻¹⁴ > 1.3 ×10⁻¹⁴ A N 43 140 1.27 × 10⁻¹¹ 1.30 × 10⁻¹¹ 0.003 0.005 3.8 × 10⁻¹⁴ < 6.5× 10⁻¹⁴ C K 25 85 1.26 × 10⁻¹¹ 1.38 × 10⁻¹¹ 0.002 0.001 2.5 × 10⁻¹⁴ >1.4 × 10⁻¹⁴ A

[0216] As noted above, the optical compensation film of Viewing AngleCompensation Integral Type Polarizing Plates E, M, and K within thepresent invention satisfy |S(md)|>|S(td)| and C(md)<C(td), and in thedimensional variation increasing direction, the photoelastic coefficientdecreases, whereby the viewing angle is minimally affected. As a result,in the evaluation of viewing angle durability, it was possible toachieve ranking A.

[0217] However, in the optical compensation film of Viewing AngleCompensation Integral Type Polarizing Plates G and N, which werecomparative examples, the photoelastic coefficient, in the dimensionalvariation increasing direction, increased resulting in variation ofphase difference. As a result, it was no possible to achieve sufficientviewing angle durability.

[0218] Viewing Angle Compensation Integral Type Polarizing Plate K,employing cellulose ester, which did not comprise the compoundsincorporating at least two aromatic rings, resulted in a high hazeproblem of the film.

Example 2

[0219] Alkyl-modified polyvinyl alcohol (0.1 μm) was applied onto oneside of each of Viewing Angle Compensation Integral Type PolarizingPlates E and G and dried by 65° C. air flow. Thereafter, an orientationlayer was prepared by carrying out a rubbing treatment parallel to themechanical direction (the absorption axis direction of the polarizer) ofthe film.

[0220] Further, Solution LC-1 having the composition described below wasapplied onto the orientation layer. The resulting orientation was firmlyfixed by exposure to 450 mL/cm³ of ultraviolet radiation under thecondition of an oxygen concentration of at least 0.1 percent.Subsequently, an optically anisotropic layer having a nematic hybridstructure was applied onto one side, whereby Viewing Angle CompensationPolarizing Plates L and 0 were prepared corresponding to each of ViewingAngle Compensation Integral Type Polarizing Plates E and G. Theaforesaid treatments were carried out through roller conveyance.

[0221] The optically anisotropic layer was placed and adhered onto theglass surface side of the liquid crystal cell. Evaluation was thencarried out in the same manner as Example 1. Viewing Angle CompensationPolarizing Plate L of the present invention resulted in a durabilityevaluation of A, while Comparative Viewing Angle Compensation PolarizingPlate resulted in an evaluation of C.

[0222] (LC-1 Composition) MEK (methyl ethyl ketone) 88 weight partsCompound 1  3 weight parts Compound 2  3 weight parts Compound 3  3weight parts Compound 4  2 weight parts

[0223] Irugacure 369 (manufactured by

[0224] Ciba Specialty Chemical Co.) 1 weight part

H₂C═CH —COO(CH₂)₄OCO—CH═CH₂  Compound 4

Example 3

[0225] Alkyl-modified polyvinyl alcohol (0.1 μm) was applied onto oneside of each of Viewing Angle Compensation Integral Type PolarizingPlates E, G, M, and N and dried by 65° C. air flow. Thereafter, anorientation layer was prepared by carrying out a rubbing treatmentparallel to the mechanical direction (the absorption axis direction ofthe polarizer) of the film.

[0226] Dissolved in 102 g of methyl ethyl ketone were 41.01 g of thediscotic liquid crystal compound described below, 4.06 g of ethyleneoxide-modified trimethylolpropane triacrylate (V#360, manufactured byOsaka Organic Chemical Industry Ltd.), 0.90 g of cellulose acetatebutyrate (CAB551-0.2, manufactured by Eastman Chemical Co.), 0.23 g ofcellulose acetate butyrate (CAB531-1, manufactured by Eastman ChemicalCo.), 1.35 g of a photopolymerization initiator (Irugacure 907,manufactured by Ciba-Geigy Corp.), and 0.45 g of a sensitizer (KayacureDETX, manufactured by Nippon Kayaku Co., Ltd.), whereby a liquid coatingcomposition was prepared.

[0227] Discotic liquid crystal compound

[0228] Subsequently, the aforesaid liquid coating composition wasapplied onto the alkyl-modified polyvinyl alcohol orientation layeremploying a #3.6 wire bar and dried for two minutes in a 130° C.constant temperature zone, whereby the discotic compound was oriented.Subsequently, the resulting discotic compound was polymerized at anambience of 60° C. by exposure to UV radiation for one minute, employinga 120 W/cm high pressure mercury lamp and allowed to equilibrate to roomtemperature.

[0229] Employing the Optical Compensation Polarizing Plates P, Q, R, andS coated with the optically anisotropic layer, were prepared werecorresponding to Optical Compensation Cellulose Ester Films D, F, H, andI. Evaluation was carried out in the same manner as for Example 2.Optical Compensation Polarizing Plates P and R achieved improvementeffects for viewing angle compensation durability, while ComparativeExamples Q and S resulted in an evaluation of C regarding viewing angledurability. As a result, in this case, the effects of the presentinvention were also confirmed.

[0230] According to the present invention, it is possible to provide anoptical compensation film exhibiting an excellent viewing anglecompensation function and to provide an optical compensation filmsupport capable of enhancing durability of the viewing anglecompensation function during storage, an optical compensation film, aviewing angle compensation integral type polarizing plate, and a liquidcrystal-display apparatus.

1. An optical compensation film comprising a cellulose ester filmcomprising cellulose ester wherein (a) each of photoelastic coefficientC(md) in a mechanical direction and photoelastic coefficient C(td) in atransverse direction of the cellulose ester film is 1×10⁻⁹ to 1×10⁻¹³Pa⁻¹, and C(md)<C(td), (b) retardation R₀ within a plane of thecellulose film defined by Formula (I) is 20 to 70 nm, (c) retardationR_(t)of the cellulose ester film in a thickness direction defined byFormula (II) is 70 to 400 nm, and (d) each of a dimensional variationratio S(md) in the mechanical direction and a dimensional variationratio S(td) in the transverse direction of the cellulose ester filmprior to and after being allowed to stand at ambient conditions of 80°C. and 90 percent relative humidity for 50 hours are −1 to 1 percent,and |S(md)|>|S(td)|. R ₀=(nx−ny)×d  (I) R _(t)={(nx+ny)/2−nz}×d  (II)wherein nx is a refractive index in a transverse direction within aplane, ny is a refractive index in a mechanical direction within aplane, nz is a refractive index in a thickness direction of the film,and d is a thickness of the film in nm.
 2. The optical compensation filmof claim 1, which comprises an optically anisotropic layer.
 3. Theoptical compensation film of claim 1, wherein the cellulose estersimultaneously satisfies Formulas (IV) and (V), 2.55≦X+Y≦2.85  (IV)1.4≦X≦2.85  (V) wherein X is a degree of substitution of an acetyl groupand Y is a degree of substitution of a propionyl group or a butyrylgroup.
 4. The optical compensation film of claim 1, wherein thecellulose ester has a degree of acetylation of 59.0 to 61.5 percent, andcomprises a compound having at least two aromatic rings in an amount of0.1 to 20 parts by weight with respect to 100 parts by weight of thecellulose ester.
 5. The optical compensation film of claim 2, whereinthe optically anisotropic layer has a fixed nematic hybrid orientationstructure.
 6. The optical compensation film of claim 2, wherein theoptically anisotropic layer contains a liquid crystal compound.
 7. Theoptical compensation film of claim 7, wherein the liquid crystalcompound is discotic liquid crystal.
 8. A viewing angle compensationintegral type polarizing plate comprising two protective films and apolarizer, wherein at least one of the protective films is the opticalcompensation film of claim 1, and a delayed phase axis of an ester filmin the optical compensation film and a transparent axis of the polarizerare substantially parallel.
 9. A liquid crystal display apparatusemploying the viewing angle compensation integral type polarizing plateof claim
 8. 10. A support for an optical compensation film comprising acellulose ester film comprising cellulose ester wherein (a) each ofphotoelastic coefficient C(md) in a mechanical direction andphotoelastic coefficient C(td) in a transverse direction of thecellulose ester film is 1×10⁻⁹ to 1×10⁻¹³ Pa⁻¹, and C(md)<C(td), (b)retardation R₀ within a plane of the cellulose film defined by Formula(I) is 20 to 70 nm, (c) retardation R_(t) of the cellulose ester film ina thickness direction defined by Formula (II) is 70 to 400 nm, and (d)each of a dimensional variation ratio S(md) in the mechanical directionand a dimensional variation ratio S(td) in the transverse direction ofthe cellulose ester film prior to and after being allowed to stand atambient conditions of 80° C. and 90 percent relative humidity for 50hours are −1 to 1 percent, and |S(md)|>|S(td)|. R ₀ (nx−ny)×d  (I) R_(t)={(nx+ny)/2−nz}×d  (II) wherein nx is a refractive index in atransverse direction within a plane, ny is a refractive index in amechanical direction within a plane, nz is a refractive index in athickness direction of the film, and d is a thickness of the film in nm.